Magnetic resonance tomographs are imaging devices which, in order to image an examination object, align nuclear spins of the examination object with a strong external magnetic field and excite them to precess around this alignment by an alternating magnetic field. The precession or return of the spins excited therefrom into a state with lower energy in turn generates an alternating magnetic field, (also described as a magnetic resonance signal), as a response, which is received by way of antennae.
With the aid of magnetic gradient fields, the signals are imprinted with spatial encoding, which subsequently enables the assignment of the received signal to a volume element. The received signal is then evaluated and a three-dimensional imaging representation of the examination object provided.
To stimulate the precession of the spin, alternating magnetic fields with a frequency corresponding to the Larmor frequency for the respective static magnetic field strength, and very high field strengths or outputs are necessary. To improve the signal-to-noise ratio of the magnetic resonance signal received by the antennae, (antennae designated as local coils may be used), arranged directly on the patient.
However, individual patients differ considerably in their physiognomy with the result that with a rigid local coil either an optimum signal is only obtained for a few patients or many local coils with different dimensions have to be kept ready.
Local coil matrices are another option, in which individual coils are arranged in a matrix. Such a local coil matrix may be flexibly designed so that it may be configured to the body shape to a certain extent. However, the flexibility is limited, for example, additional openings for limbs cannot be provided flexibly in such a local coil matrix. If, on the contrary, the limbs are wrapped with the flexible local coil matrix, the ends overlap and alter the high frequency properties and impair image acquisition.